It is forty years since I was at Craig y Nos, and to put it mildly my memories don't fit at all well with what I now see on Google Earth. However if the collapse was in the car park at the north end of the site it is geologically promising, going into the Dowlais Limestone a short distance from the underlying mudstone, more likely perhaps is the car park to the south although the CCR map overlay suggests this is more on the mudstone. Interesting enough in any case to be worth a look.

I pooped in as I was driving by Craig a Nos today, the hole is about 6ft diameter and about 3-4 ft deep with no obvious ways on, so I guess the collapse must have been much deeper down the hole and all what we can see is the top of it.

My sister in law reported hearing a news item that mentioned a stream flowing at the bottom of the hole. The owner of the castle has said "the culvert" would be repaired. The collapse was in the "overflow car park", in other words the southern one where staff also park their cars (the car belonged to a staff member).

I guess therefore it is a collapse into the culvert taking the water from Hospital Cave from the Riding Centre site under the castle car park en route to the Afon Tawe. So nothing for us to get excited about.

More often that not 'sinkholes' reported in the media are nothing to do with caves. They are usually collapsed drains/culverts/sewers, burst water mains, or in some cases old mines or shafts. Only rarely are 'sinkholes' reported in the press natural cavities.